1. A substance is a being that is capable of action. It is either •simple, meaning that it has no parts, or •composite, meaning that it is a collection of simple substances or monads. (Monas is a Greek word meaning ‘unity’ or ‘oneness’.) Any composite thing—any body—is a multiplicity, ·a many, but simple substances are unities, ·or ones·. There must be simple substances everywhere, because without simples there would be no composites—·without ones there could not be manies·. And simple substances are lives, souls, minds—·where there is a simple substance there is life·—and the world’s being full of such substances means that the whole of nature is full of life